The present invention relates to a linear motor system and a driving apparatus driven by the linear motor system as a driving source.
In recent technology, a positioning table for performing a positioning through guidance of a linear motion of a table has been widely utilized for, or applied to, machine tools, industrial robots, and like, machines or mechanisms.
According to an increased requirement for operating the table at a high speed, a linear motor has been often utilized in place of a ball screw as a driving source. In general, the linear motor is provided with a movable element as a primary side and a stator as a secondary side. The primary movable element is given a thrust (force) by the change of a field (magnetic field) and then linearly moves on the secondary side stator.
In order to move the table fast, it is desired for the linear motor to generate a large thrust force. There is known, as a linear motor having an increased large thrust force, a linear motor in which a pair of primary movable elements disposed on both sides of a single secondary stator so as to sandwich the same therebetween.
However, in such a known type linear motor, since the primary movable elements are arranged on both sides of the secondary stator, the thickness thereof is increased accordingly, which is not advantageous.
An object of the present invention is to substantially eliminate the defect or drawback encountered in the prior art and to provide a linear motor system capable of generating a large thrust force without increasing the thickness of the structure thereof and also provide a driving apparatus provided with such linear motor system as a driving source.
This and other objects can be achieved according to the present invention by providing, in one aspect, a linear motor system comprising:
a first linear motor having a primary side being mounted to either one of first and second movable elements which are relatively movable with respect to each other; and
a secondary linear motor having a secondary side mounted to this one of first and second movable elements so as to extend in the relatively movable direction to be continuous to the primary side of the first linear motor,
the second linear motor having a primary side mounted to another one of the first and second movable elements, and
the first linear motor having a secondary side mounted to the another one of the first and second movable elements so as to extend in the relatively movable direction to be continuous to the primary side of the second linear motor.
According to the structure of the linear motor system of this aspect, since two linear motors are accommodated, the thrust force can be increased twice. Moreover, the excitation is made average to thereby operate the system more smoothly. Furthermore, since the second linear motor is assembled to the first linear motor in a reversed manner, the thickness of the entire structure of the linear motor system can be effectively made thin.
In a preferred embodiment of this aspect, the first and second linear motors are composed of linear induction motors or linear pulse motors, respectively, in which the secondary sides of the respective linear induction motors are arranged so as to oppose to each other.
The first and second movable elements may be composed of outer and inner rail members which are relatively movably fitted to each other, and the first and second linear motors are arranged between the outer and inner rail members.
In a case where linear D.C. motors are used for the first and second linear motors in the above linear motor system, in which a distance between the secondary side magnets is short, there may be caused a defect of operation because of the generation of an A.C. magnetic field between magnets. According to the preferred embodiment of the above aspect of the present invention, however, a linear induction motor or linear pulse motor having no magnet means is utilized as the secondary side, so that no alternating magnetic field is generated. However, a linear D.C. motor may be utilized as far as there is adopted a structure in which the distance between the secondary sides of the first and second linear motors can be made relatively large.
In another aspect of the present invention, there is provided a driving apparatus comprising:
first and second movable elements which are relatively movable with respect to each other; and
a driving unit for giving driving power to the first and second movable elements, the driving unit comprising a linear motor system, which comprises:
a first linear motor having a primary side being mounted to either one of the first and second movable elements which are relatively movable with respect to each other; and
a secondary linear motor having a secondary side mounted to this one of the first and second movable elements so as to extend in the relatively movable direction to be continuous to the primary side of the first linear motor,
the second linear motor having a primary side mounted to another one of the first and second movable elements, and
the first linear motor having a secondary side mounted to the another one of the first and second movable elements so as to extend in the relatively movable direction to be continuous to the primary side of the second linear motor.
According to the structure of this driving apparatus, since two linear motors are accommodated, the thrust force can be increased twice. Furthermore, since the improved linear motor system is provided, the excitation is made average to thereby operate the system more smoothly, and since the second linear is assembled to the first linear motor in a reversed manner, the thickness of the entire structure of the linear motor system can be effectively made thin.
In a preferred embodiment of this aspect, the driving apparatus may further comprises first and second guide units for guiding the second movable element in the relatively movable direction with respect to the first movable element, the first guide unit being provided for the first movable element and the second guide unit being provided for the second movable element, and wherein the first linear motor generates a thrust force at a position which is substantially the same position of the first guide unit in the relatively movable direction, and the second linear motor generates a thrust force at a position which is substantially the same position of the second guide unit in the relatively movable direction.
The primary side of the first linear motor is operatively connected to the first movable element, the first guide unit is fixed to the first movable element at a portion in a vicinity of the primary side of the first linear motor in the relatively movable direction, and the primary side of the second linear motor is operatively connected to the second movable element, and the second guide unit is fixed to the second movable element at a portion in a vicinity of the primary side of the second linear motor in the relatively movable direction.
The first and second linear motors are composed of linear induction motors or linear pulse motors respectively, in which the secondary sides of the respective linear induction motors are arranged so as to oppose each other.
The first and second movable elements may be composed of outer and inner rail members which are relatively movably fitted to each other and the first and second linear motors are arranged between the outer and inner rail members. The inner rail member includes a first inner rail and a second inner rail which are assembled to be relatively movable.
The first movable element may be a flat rectangular base and the second movable element may be a flat rectangular table, the base and table being assembled to be slidable to each other.
According to such preferred embodiment, the thrust force can be generated at the same position as the position of the guide unit irrespective of the position of the first movable element with respect to the second movable element. For this reason, even if the respective linear motors generate thrust components in directions other than the relatively movable direction of the movable elements, the guide unit positioned on the thrusting point can surely load the thrust components in the directions other than the relatively movable direction. Accordingly, the first movable element can be smoothly moved with respect to the second movable element. Further, in a case where the thrust is not generated at the same position as that of the guide unit, moments will be caused to the respective movable elements by the thrust components in the directions other than in the relatively movable direction, and such moments disturb the smooth movement of the first movable element with respect to the second movable element. Such defect can be eliminated by the above structure of the present invention.
Furthermore, a relatively wide distance can be ensured between two guide units in an optional attitude of the first movable element with respect to the second movable element, so that the driving apparatus of this embodiment can also load the moment load.
Still furthermore, the first and second linear motors may generate the thrust forces at the same positions of the first and second guide units, respectively.
The nature and further characteristic features may be made more clear from the following descriptions made with reference to the accompanying drawings.